1. Field of the Invention
The present invention relates to a portable communication apparatus which is operated using a battery as a power source, and more specifically to a portable telephone unit and a portable facsimile unit.
2. Description of Related Art
Recently, a portable telephone unit has been popularized, and further a portable facsimile unit has been contrived in which a transmit-receive function of an image is added to the portable telephone unit. Since such a portable communication apparatus depends on a battery for a power source, it is important to design the portable communication apparatus so as to adequately cope with battery run-out part way through a communication in order to enhance the convenience of such a portable communication apparatus. When the battery run-out occurs during the communication, the line is cut off and the communication operation has to be restarted to connect the line after the battery is replaced.
Particularly, in the portable facsimile unit, if a battery runs out in the middle of transmission after reading the content of an original, accounts are imposed twice for a single original, thus being uneconomical.
For example, European Patent Publication No. EP 536043 discloses an idea in which an image communication apparatus using a battery as a power source is provided with means for alarming a user by an LED or a buzzer that a voltage of the battery has dropped. By this configuration, it is possible to avoid the situation that results in a defective communication due to run-out of power in the battery during the communication.
However, the prior art described in the above publication merely operates when a voltage of a battery drops to a level below a predetermined threshold and the user is alarmed to replace the battery. Accordingly, even after an alarm is made, a possibility remains that a communication of a short content, for example a letter for one or two pages can be transmitted.
Further, since an alarm is merely made, even if such an alarm is made, the user would sometimes operate a facsimile transmission for a relatively large amount of documents. In this case, a battery run-out may occur part way through the communication, resulting in an error of communication. Therefore, in order to avoid an occurrence of communication error caused by the battery run-out, it is necessary to provide a configuration that the alarm as described above be made in the state where a predetermined residual amount of the battery still remains. If so, when a battery is replaced at the time when the alarm as described above is made, waste of the battery increases.